Most episodes end with Diamond at the piano, singing a standard, popular song, or showtune from Powell's repertoire to Helen Asher (his girlfriend) in her penthouse at 975 Park Avenue.

[2] The television debut of Richard Diamond occurred on November 22, 1956, when Don Taylor portrayed the character in the "Double Cross" episode on Chevron Hall of Stars.

[citation needed] David Janssen, before The Fugitive, starred as Diamond, a former officer of the New York Police Department and a hard-boiled private detective in the film noir tradition.

After the first season when the sponsor was Maxwell House, the show was sponsored by Kent cigarettes, and Frank DeVol’s playfully mysterious theme was heard underneath an announcer hawking either "Maxwell House – Good to the Last Drop" or “Kent with the Micronite filter.” In syndicated rebroadcasts of the series, the revised title, Call Mr. D., flashes on the screen, and DeVol's music is replaced by Pete Rugolo’s far more recognizable theme—although that did not appear until Season 3.

The 18 episodes comprising Season 3 aired from February to mid-June of 1959, and Diamond’s character now bore only slight resemblance to his California-based noirish predecessors Sam Spade and Philip Marlowe.

By the late 1950s, the glamour of Hollywood was becoming an irresistible fantasy for millions of viewers, and the popularity of Warner Brothers’ 77 Sunset Strip—which involved a good deal of location shooting and began airing four months before Diamond's third season—undoubtedly influenced a newer P. I. image that often seemed more inspired by Hugh Hefner than by Dashiell Hammett.

With panoramic sliding glass doors providing views of the mountains and the city, his sunken living room featured a bar and a loveseat, where he could be found many evenings entertaining young women before a fire.

The Hefner-like fantasy was enhanced by gadgets, especially Diamond's car phone, which connected him directly to an answering service overseen by the shapely, enigmatic “Sam.” Season 3's modern, more youthful ambience was complemented by a jazz score by composer/arranger Pete Rugolo, who created a set of big-band, Stan Kenton-esque cues for each of the episodes.

In the highly stylized opening sequence, Rugolo's robust theme is preceded by tense melodic fragments underscoring a series of frenetic, silhouette images of Diamond running, before walking forward—again in hat, suit, and tie—to light a cigarette, suggesting a re-boot of the original noirish conception.

Though the opening titles remained, Rugolo's score was replaced by a more sedate theme, "Nervous" by Richard Shores, later to be used during the highlight sequence that began every episode of The Dick Powell Show.